Analysis of variance(ANOVA), developed by Ronald Fisher is a method used to statistically measure the difference between means of different variables. While the t test measures difference between two population means, analysis of variance measures the difference for more than two population means. There is the one way ANOVA and two way ANOVA that test the difference between means.
The answer would probably be 18 degrees below normal because the absolute values of the rest are 8 not 18 which is the absolute value of 18 degrees below normal.
